1. Field of the Invention
The present invention relates to a process for preparing polymer based granules each presenting a shaded appearance of anisotropic colouring. A xe2x80x9cshaded appearance of anisotropic colouringxe2x80x9d should read as meaning random variations of colouring observable in all directions from any given point in the body of the granule. The present invention also relates to polymer granules presenting such a shaded appearance of anisotropic colouring. Such granules can, in particular, be obtained through the use of said process. The present invention also relates to the applications of these granules, in particular for producing surface coatings.
2. Prior Art
Various methods are known for producing cast surface coatings based on polymer granules incorporated in a resin binder. One can thus obtain a cast surface coating that is essentially inalterable under usual conditions of wear, and the visual appearance of which is of the mosaic, single colour or multicoloured type.
By way of example can be mentioned patent application FR 2 541 296 which describes such cast coatings based on rubber granules that can be coloured and which are spread in an entirely random fashion and inserted into a binder.
For this purpose, processes for manufacturing polymer based granules used, for example, to manufacture cast coatings, are known and usually include steps of mixing a base polymer with additives, of extrusion, of calendering or some other shaping, of vulcanization and of cooling of the mixture before its grinding. Furthermore, the granules are usually coloured by adding a colorant or a mixture of colorants. The aim of the usual applications is to obtain granules of a homogenous colour. Multi-coloured surface coatings are, indeed, obtained by mixing several colours, or shades of colour, of granules obtained during successive manufacturing operations.
Thus, all the granules of each manufacturing operation are identical, with an isotropic colouring, that is to say homogenous in the body of each granule, and the coatings that can be obtained with these granules have the drawback of having an artificial visual appearance, because being uniform, in comparison with natural solid materials such as, for example, marble or stones or the like, whether crushed or not.
Moreover, polymer based in-works manufactured materials, for example polymer surface coatings presenting shades of colouring are known in the prior art. However, such shades of colouring are obtained through the dispersion of an added layer of colorant on the surface or by encrusting coloured materials. Such manufactured materials are made in their final form by equipment conferring thereupon the desired specific forms, for example slabs or tiles of varying size and thickness, or widths. However, this aforementioned technique is confined to materials manufactured according to the desired final form. Furthermore, in the case of such manufactured materials, there can be no question of sanding or buffing to renovate the appearance thereof.
By contrast with these manufactured materials, there is a growing need in this field for obtaining surface coatings cast in situ, that is to say prepared directly on the work site, based on polymer granules combining mechanical characteristics that are satisfactory in various fields of application, in particular for pedestrian use, and a visual appearance presenting a certain variety of colours or shades of colouring that are anisotropic in the body of the granules, hence of the coating obtained from such granules.
The present invention enables to achieve this result through a particularly simple and inexpensive process.
The process for manufacturing polymer granules includes the operations of mixing a base polymer and additives, with a specific step of adding shading colorant to the polymer mixture followed by a step of carrying out an incomplete homogenization of the colorant with the polymer mixture, the duration of which is fixed according to desired colouring anisotropy characteristics, the process providing granules having such an anisotropy which can be used for the manufacturing of coatings and moulded articles.